The present invention relates to a prosthetic implant for attachment to a bone inside the body for replacing a bearing surface. More particularly, the present invention relates to a locking assembly for rigidly attaching a bearing component to a base component which has been attached to a bone.
Various methods are known in the art for securing a bearing component to a base component. One such method is disclosed in U.S. Pat. No. 4,257,129. In this device, a pin is inserted through a hole in the bearing component and into a base component. A clip member is then inserted into a slot formed in the bearing component. The clip member engages the pin to hold the bearing component in place on the base component.
U.S. Pat. No. 4,795,468 discloses another known method for locking a bearing insert to a base support of a prosthetic implant. The implant includes a resilient locking clip which is positioned in a cavity formed on one side of the base support such that when the bearing insert and the base support are assembled together, the clip extends from the cavity to lie within a groove formed on an edge of the bearing insert to secure the two components together.
Yet another method of attaching a bearing component to a base component is to compression mold the bearing component onto the base component. The bearing component cannot be removed from the base component without destruction of the bearing component. Therefore, the bearing component cannot be changed without also changing the base component.
According to the present invention, a prosthetic implant assembly is provided. The assembly includes a base component including means for securing the base component to a bone and a generally planar surface having a recessed portion formed therein. The assembly also includes spring means situated in the recessed portion of the base component. The spring means includes a tab extending away from the spring means. The assembly further includes a bearing component including means for slidably engaging the base component to couple the bearing component to the base component and means for receiving the tab of the spring means therein to lock the bearing component in a fixed position relative to the base component.
The recessed portion of the implant assembly includes a first section having a predetermined, substantially uniform depth and a second section having a depth greater than the depth of the first section. The spring means includes a spring clip having a thickness substantially equal to the predetermined depth of the first section to provide a cantilevered spring within the recessed portion. The tab extends away from an end portion of the spring clip located within the second section of the recessed portion and the means for receiving the tab includes a groove formed in a bottom surface of the bearing component for receiving the tab therein.
The assembly further includes a ramp surface formed along a side of the bearing component in close proximity to the means for receiving the tab. The ramp surface is configured to engage the tab of the spring clip and to force the tab along with a portion of the spring clip downwardly into the second section of the recessed portion as the bearing component slides relative to the base component during installation of the bearing component. The tab and the portion of the spring clip move upwardly toward the bearing component after the receiving means is situated over the tab so that the tab enters the receiving means and locks the bearing component in a predetermined position relative the base component. A hole is provided in the bearing component at a position over the spring clip to provide an access opening to permit the tab to be disengaged from the receiving means to permit removal of the bearing component from the base component.
The present invention advantageously provides an assembly for locking a bearing component to a base component which uses few parts and is easy to construct. The bearing component can be rigidly fixed to the base component, but can be easily removed. Therefore, the variety of sizes or styles of bearing components can be inserted onto the base component and inspected to determine which bearing component best fits a patient's particular needs after the base component is implanted in a bone.